Mark - you mentioned character development and training. I used to say - without tongue in cheek - that I would much prefer the guys in the kick-boxing gym baby-sitting my kids than a lot of people I knew in trad. martial arts/aikido. Reality testing makes you face who you really are- and this often maakes a more trustworthy individual.
But training in aiki is a puzzle, isn't it? It is what you make of it, what you are made of, and what it makes you. Take Sagawa Yukiyoshi. I know two people who met him personally, and both told me what a thoroughly unpleasant man he was. Take Inoue, Osensei's nephew. Another very unpleasant, narcissistic man, by many accounts. Shioda was often a brutal sadist. Tohei was often grandiose and self-involved. Tomiki was a thorough gentleman. Mochizuki was an exemplary man. Kodo Horikawa was, at least by some of the accounts I have heard, a humble, straightforward man, but some of the people in his own organization are anything but.
Me personally - aikido was not really of help to me in confronting my demons or making me more pleasant. Quite the opposite, really. Araki-ryu and kick-boxing had a far more positive effect on me.
I think, in the long run, it's what you bring to a study and how it effects you - but I do not think there is anything of predictable benefit - or harm. I think some people will train in "good aiki" and become even more manipulative, aggressive, unpleasant, grandiose or self-involved than they were before. Others would experience a kind of inescapable self-confrontation and change in a positive manner. Others - most, I bet - would be exactly the same, only more skilled with their bodies.
Best
Ellis Amdur